The combination of the Olympics and the Colorado theater massacre is having a sizeable impact on weekend box office sales, which could end 30 percent down from last year.

Twentieth Century Fox's high-profile summer comedy The Watch -- starring Ben Stiller, Vince Vaughn, Jonah Hill and Richard Ayoade -- debuted to a sluggish $4.5 million Friday, well behind the $19 million earned by The Dark Knight Rises on its second Friday. The R-rated pic earned a dismal C+ CinemaScore.

The weekend's other new entry is Summit Entertainment's 3D dance pic Step Up Revolution, which grossed $4.9 million to beat The Watch. Step Up 4 earned a B+ CinemaScore.

Most box office observers predict that The Watch will pull ahead of Step Up 4 and gross in the $13 million to $15 million range for the weekend, compared to $11 million to $12 million for the Summit film (Disney released the previous three titles in the Step Up series).

Heading into the weekend, research firm NRG warned Hollywood studios that 20 percent to 25 percent of the moviegoing audience were hesitant to see a movie this weekend because of the Colorado shooting (to boot, tracking was already soft for The Watch). The Olympics also are keeping consumers at home.

By any measure, Dark Knight Rises continues to do big business, but there is no doubt the tentpole is leaving business on the table because of the shooting during a midnight screening of the movie. The film, which is now pacing behind The Dark Knight, is expected to earn in the $59 million range for the weeked, compared to a $75 million second weekend for Dark Knight.

Dark Knight Rises, from Warner Bros. and Legendary Pictures, ended Friday with a cume of $243 million. At the same point in time Dark Knight had grossed $261.8 million domestically.

Friday over Friday, Dark Knight Rises fell 76 percent, in line with other films that had sizeable midnight earnings on opening day (the pic collected $30.6 million in midnight grosses).